This invention relates to novel fluoran derivatives and to the use thereof as electron donative color forming substances in pressure sensitive, heat sensitive and electrothermal sensitive recording sheets.
There have been proposed hitherto various kinds of recording (copying) systems for transmitted information wherein a color forming reaction between a colorless or light color basic chromogenic material and an electron accepting organic or inorganic material is utilized, and mechanical, heat, electric or light energy serves as a medium. Among them there are included a pressure sensitive copying sheet, a heat sensitive recording sheet, an electrothermal sensitive recording sheet, an ultrasonic recording sheet, an electron beam recording sheet, an electrostatic recording sheet and a photosensitive recording sheet as described in JAPAN TAPPI vol. 30, pp. 411-421 and 463-470 (1976).
There are found various proposals for the utilization of those kinds of recording (copying) systems in photosensitive printing compositions, typewriter ribbons, ball-point pen ink, crayon and stamp ink.
In such recording systems, utilizing the color reaction between an electron donating color forming material (hereinafter referred to as "color former") and an electron accepting color developing material (hereinafter referred to as "acceptor"), images showing various hues may be obtained by using various kinds of color formers. There is now an increased demand for recording systems by which black color images capable of being reproducible for copies may be obtained. Theoretically, images of substantially black color may be obtained by using a mixture of various color formers which will develop into the respective hues of different colors such as red, blue, yellow and green. The utilization of a mixture of various color formers for obtaining a black color has, however, a disadvantage that the once developed black color images can not be maintained for a long period of time because the color formers employed are respectively different in their color developing speeds and their color fastnesses against light, temperature and moisture. In consequence, some attempts have been made hitherto to obtain images of substantially black color with the use of a single color former. However, there has not yet been found any such color former capable of developing a substantially black color image that always satisfies all of the requirements for stability before its color development, its color developing speed, its color fastness, its color hue, its color image as developed and its production costs.
The primary object of this invention is to provide novel fluoran derivatives.
Another object of this invention is to provide novel fluoran derivatives which are useful as color formers in various recording sheets.
Another object of this invention is to provide novel color formers for use in recording sheets in which the color images as developed assume a substantially deep-black color and have a good light resistance.
A further object of this invention is to provide novel color formers for use in heat sensitive or electrothermal sensitive recording sheets which give substantially no fogging on the record materials to which they are applied.
A still further object of this invention is to provide novel color formers for use in pressure sensitive recording sheets which possess a good and instant color developability.
It is also included among the objects of this invention to provide an improved moisture resistant recording sheet in which a fluoran derivative as a new compound is used as a color former and the color images as developed thereby possess a good light resistance and assume a substantially deep-black color which is suitable for reproduction of copies.